This paper revisits the notions of lexical category and category change from a constructionist perspective. I distinguish between four processes of category change (affixal derivation, conversion, transposition and reanalysis) and demonstrate how these category-changing processes can be analyzed in the framework of Construction Grammar. More particularly, it will be claimed that lexical categories can be understood as abstract instances of constructions (i.e., form-function pairings) and category change will be assumed to be closely connected to the process of constructionalization, i.e., the creation of new form-meaning pairings. Furthermore, it will be shown that the constructionist approach offers the advantage of accounting for the variety of input categories (ranging from morphemes to multi-word units) as well as for some problematic characteristics related to certain types of category change, such as context-sensitivity, counterdirectionality and gradualness of the changes.